To silence vibration noise due to vibration of a vibration noise source such as a machine and vehicle by the active noise control, a technique is disclosed which mounts an acceleration sensor on the vibration noise source, and refers to the acceleration detected (see Patent Document 1, for example).
However, the vibration of an object is not always limited to a single direction of motion, but has a plurality of vibration components of different directions of motion such as vertical and horizontal directions. At this time, it is conceivable due to design reasons that the direction of motion of the vibration to be detected does not always agree with the axis of the acceleration sensor (that is, the detection direction of the acceleration). Considering such a case, a technique is disclosed which measures deviation of the axis of the acceleration sensor from the direction of motion of the vibration to be detected, and corrects the output value of the acceleration sensor in accordance with the deviation (see Patent Document 2, for example).
The technique of the Patent Document 2, however, cannot deal with the case where the deviation between the direction of motion of the vibration that contributes to the noise and the axis of the acceleration sensor is not fixed and varies depending on conditions. With respect to the problem, a Patent Document 3, for example, discloses a technique that measures the direction of motion from an arctangent based on a ratio between the accelerations of the individual axes using an acceleration sensor that detects the accelerations of two axes orthogonal to each other.